Uptake of barium and strontium by cress ( Lepidium Sativum) in water culture and the presence of an inhibiting soluble factor

Abstract

Seeds of cress were sown in various densities on plastic grids placed in half-litre dishes filled with either a dilute salt solution or distilled water. After 2 days the radionuclides 133Ba, 134Cs and 85Sr were added, and after another 5 days the plants were harvested and the radioactivity measured by γ-ray spectrometry. It was found that plants grown in low density cultures took up more than ten times the activity of Ba and Sr than plants in dense cultures. In a second experiment, plants were grown in non-radioactive medium for 5 days and then some of the plants were changed so that the sparse culture was placed in the dish which previously contained the dense sulture and vice versa. The radionuclides were then added. These plants in alternated sparse cultures concentrated less radioactivity of Ba and Sr than the corresponding non-alternated cultures. Furthermore, when water from very dense cultures on which plants had grown for a week was sterile-filtered and added to fresh cultures, it was shown that this conditioned water strongly inhibited the uptake of Ba and Sr, although the concentration of “conditioned water” was only 15% of the total volume. The difference in radionuclide concentration in the plants as a function of plant density disappeared when the concentrations of Ca and Mg in the nutrient solution were raised to 0.15 and 0.40 mM, respectively. Apparently a chelating substance, possibly excreted from the plant roots, is responsible for the inhibition of the uptake of bivalent cations, and this agent becomes saturated when bivalent cations are present at sufficiently high concentrations.